This project is designed to evaluate the nature of lactogenic hormone receptors and the factors (including other hormones) which affect binding of the hormone to this molecule. Studies include 1) purification of the receptor and preparation and characterization of an antibody against it; 2) examination of the nature of the interaction of prolactin and human growth hormone with native as well as cryptic forms of the receptor; 3) characterize the selectivity of the effect of changes in the membrane lipid environment on binding of lactogenic hormones to their receptors vs other peptide hormes (such as EGF) binding to their receptors, and 4) examining the metabolism of prolactin by its target tissue.